Transportation systems are often expected to overcome long distances and to cross areas where suitable power generation systems are not available. Direct current (DC) transmission is a suitable transmission method for economic power transmission over such long distances.
DC transmission systems are known for energy transfer between two remote systems. Thereby, a first converter station is usually located close to the power generation unit at one end of a DC transmission line and a second converter station is located at the other end of the DC transmission line in the load center.
Some more sophisticated DC transmission systems comprise bidirectional converter stations and allow for controlling the current flow direction through the bidirectional converter stations.
Worldwide transportation produces a huge amount of carbon dioxid emissions and thus has a negative impact on the environment. It is therefore desirable to provide transportation systems, especially railway vehicles, with energy from renewable energy sources.
However, transportation systems have to be highly reliable. Renewable energy sources, on the contrary, are intermittent and their energy output quantity fluctuates.
Besides, the power demand of transportation systems usually fluctuates too because the vehicles start and stop regularly.
It is therefore the object of the present invention to provide an energy storage and transmission system which allows for compensating fluctuations of energy supply and demand.
This object is achieved by means of the independent claim. Advantageous features are defined in the dependent claims. Further objects and advantages are apparent in the following detailed description.